Dimethyl carbonate (DMC) is an important intermediate and is widely used in industry. Owing to its low toxicity, dimethyl carbonate is considered a “green” chemical product with bright development prospects. DMC is a versatile chemical and has been used mainly as a methylating and methoxy carbonylating agent as a safe substitute for dimethyl sulphate, phosgene or methyl halide, which are toxic or corrosive. It can also be used as a solvent to replace halogenated solvents. DMC has a potential application as fuel additive for gasoline to improve octane number and could lead to increase in demand of DMC. This increasing focus on the use of DMC is mainly due to the bio-degradability, with a low bioaccumulation as well as its low toxicity.
US 20140094621 A1 discloses a method for preparing dialkyl carbonate from urea or alkyl carbamate and alkyl alcohol using a metal oxide catalyst selected from the group consisting of CaO, MgO, ZnO, PbO, La2O3, Y2O3 and hydrotalcite and an ionic liquid comprising a cation, which produces a hydrogen ion, and a hydrophobic anion containing fluorine with high temperature stability.
WO 2009/052996 A1/US 20100312001 A1 A catalyst for the synthesis of an organic carbonate comprising a calcinate prepared by calcining a rare earth element containing hydrous salt at a calcining temperature within the range of 150° C. to 450° C.
Article titled, “CeO2-ZrO2 Solid Solution Catalyst for Selective Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide” by Keiichi Tomishige in Catalysis Letters, September 2001, Volume 76, Issue 1, pp 71-74 reports CeO2—ZrO2 solid solution catalysts are very effective for the selective synthesis of dimethyl carbonate from methanol and CO2. The activity was much dependent on the calcination temperature. The higher the calcination temperature, the higher the activity of the catalyst for DMC formation, though the BET surface area is lower on the catalyst calcined at higher temperature
Article titled, “Effect of the preparation method on the properties of zirconia-coria materials” Sylvie Rossignol, François Gérard and Daniel Duprez J. Mater. Chem., 1999, 9, 1615-1620 reports Zirconium-cerium mixed oxides were prepared by two Methods: (i) sol-gel hydrolysis of alcoholic solutions of zirconium alkoxides (n-propoxide and n-butoxide) in the presence of aqueous solutions of cerium nitrate (method SG) or (ii) coprecipitation of aqueous solutions of zirconyl and cerium nitrates by ammonia (method NP).
Article titled, “Synthesis of Dimethyl Carbonate from Urea and Methanol over Solid Base Catalysts” by Wang M H et al in Catal Commun, vol 7, pp 6-10, 2006 reports CaO as catalyst.
CN 1416949 A discloses synthesis of dimethyl carbonate from urea and methanol with a metal oxide catalyst, wherein: it is made of lithium, magnesium, nickel, zinc, lead, iron, aluminum, molybdenum, zirconium, lanthanum metal oxides 1-3 composition; wherein the mixed metal oxide catalyst must be zinc oxide as the main body, the percentage by weight of 35 to 95%, by weight of the other metal oxides and from 5 to 65%, when the catalyst is a mixed metal oxide in three, the other two metal oxides other than the percentage by weight of zinc oxide as 1:1.
US 20060047136 A1 discloses A catalyst for the preparation of dimethyl carbonate from urea and methanol, characterized in that the catalyst has a composition on weight base of: active component: from 20 to 50 wt % and carrier: from 80 to 50 wt %,
Wherein, the carrier is selected from the group consisting of active carbon, α-alumina, γ-alumina, silica, and molecular sieve; and the active component is one or more selected from the group consisting of oxides and chlorides of alkali metals, alkali-earth metals, and transition elements.
U.S. Pat. No. 4,436,668A discloses Carbonates prepared by reacting carbamic acid esters with alcohols at above 140° C., wherein the ammonia formed is stripped from the reaction mixture during the reaction.
U.S. Pat. No. 6,162,940 A discloses a method for co-producing dialkyl carbonate and alkanediol by reacting alkylene carbonate with alkanol in the presence of a complex salt catalyst having a formula Ax (My Oz), wherein A is an alkali metal or alkaline earth metal, M is a Group 5 or Group 6 transition metal, O is oxygen, x is 1 or 2, y is 1 or 2, and z is an integer from 3 to 6.
EP 0478073 A2 discloses a process for producing a dialkyl carbonate by contacting an alkylene carbonate with an alkanol in the presence of a mixed metal oxide catalyst or a modified bimetallic or polymetallic catalyst.
WO 2015132801 A1, WO 2014072803 A1 and WO 2014072802 A2 disclose other routes for synthesis of dimethyl carbonate and related compounds using different catalysts.
The main disadvantages of the reported routes are: the slow reaction rate of epoxides with CO2 and requirement of high pressures, and the exchange reaction of the cyclic carbonate with methanol are limited by equilibrium. The economy of the processes is affected due to the use of epoxide which is expensive and formation of ethylene glycol as a by-product in stoichiometric quantity.
Therefore, it is the need to develop an efficient process for the synthesis of dialkyl carbonates.